Brady Aiken, the first overall pick in Thursday’s draft and the Astros’ newest prized prospect, threw the greatest game of his young career in September in Taichung, Taiwan, a full day away from home.

Astros fans were treated to a glimpse of the future Thursday when Brady Aiken was shown on Minute Maid Park’s big screen shortly after being selected No. 1 overall in the draft. (Karen Warren / Houston Chronicle )

The Astros scouted Aiken for three years, but they didn’t make it that far. The polished lefty struck out 10 in seven innings to clinch a championship, for USA Baseball’s 18-and-under team, 3-2 over Japan.

Back at the hotel afterward, Aiken didn’t want congratulations — only a piece of a paper.

“I used to share with the team motivational stories, just different things during that time in Taiwan, and one of them was about a prisoner of war,” said the team’s coach, Rob Cooper. “I shared with the team about how this guy envisioned himself playing golf every single day, 36 holes. I’ll never forget, (Aiken) asked me after I said it: ‘Hey coach, can I get a copy of that? I want to take that back with me and share that with my team back home.’

“Well, we win a gold medal. We get back to the hotel, and I happen to have my folder with me, and I have the copy that I used. I said, ‘Hey Brady, you want this copy?’ … He goes, ‘This is going to be a great way for me to remember these guys and this team.’

“That’s who he is.”

The word “makeup” came up over and over Thursday at Minute Maid Park after the Astros chose Aiken, a 17-year-old lefthanded pitcher from Cathedral Catholic High School in San Diego, Calif., as the first overall pick in MLB’s 2014 first-year player draft. He completes the Astros trifecta of consecutive top selections in the draft, joining an exclusive club with the brilliant Carlos Correa (2012) and struggling Mark Appel (2013) that is not expected to expand to a quartet next year.

“Unbelievable, it’s really a dream come true,” Aiken said. “This is something that I’ve wanted ever since I was a young kid and it’s really — it’s real. I’m at a loss for words. This is my dream, and it’s finally starting to come true.”

He said his selection came as at least something of a surprise, although in recent weeks, the industry consensus was that Aiken would be the Astros’ choice. The Astros didn’t get cute.

“We were negotiating a little bit before the draft, there was a couple people in the running,” Aiken said. “We didn’t know until it came on TV.”

As a pitcher, the 6-3, 210-pound Aiken is remarkably advanced, and he had to be for the Astros to take a high school arm at the highest possible position. Prep pitchers are inherently riskier than college pitchers, because there’s more time before they reach the majors and simply a smaller body of work to evaluate.

How’s this for high praise?

“This is the most advanced high school pitcher I’ve ever seen in my entire career,” general manager Jeff Luhnow said. “He has command like I’ve never seen before.

“The reason he was (ranked) so high last year was because of his command and pitchability, and then his stuff took a tick up as he came into this year, and that’s when he just exploded.”

Aiken’s fastball sits at 92-93 mph, reaching 96-97 mph at its peak. He isn’t blow-you-away overpowering, at least not at this stage of his career, but he has poise, command and approach. He’s projectable, low-effort — essentially, any positive term one can label a young pitcher applies to Aiken, aside from “flamethrower.”

“I throw a four-seam and a two-seam fastball, and then I throw a curveball and a changeup,” Aiken said. “I started throwing the cutter a little, bit but then I decided to lay off because of all the arm injuries that are happening. … My game is around going after the hitter, being aggressive and commanding the plate and commanding all my pitches.”

Aiken doesn’t profile as the second-coming of Randy Johnson. But, southpaws in particular don’t require the absolute best velocity to become aces. Plus, Aiken is so young.

“He struck out almost two batters an inning in his high school season, so he’s very dominant at the high school level,” Astros scouting director Mike Elias said. “If you’re asking in terms of stuff, he’s got plus stuff and it’s stuff that can develop into overpowering stuff at the major league level. But he’s lefthanded. He doesn’t throw 100 (mph), but he has a plus arsenal that I think is going to strike out hitters at this level, and contend to be one of the best pitchers in this league.”

Aiken is just the fifth lefty selected first overall since the draft started in 1965, and the first since the Tampa Bay Rays took David Price first overall in 2007.

What a coincidence: asked what pitchers he could be compared to, Aiken cited two elites, Price and Clayton Kershaw of the Los Angeles Dodgers. Cole Hamels and Andy Pettitte are likenesses that the Astros saw, area scout Brad Budzinski said.

As injury concerns for pitchers rampage the game, Aiken was used appropriately in the three years the Astros followed him. He averaged about 80 pitches per outing, Budzinski said.

“We feel in the category of high school pitchers, this is about as safe a player as you can have,” Luhnow said. “Because he’s got the polish, he’s got the stuff, he’s got the command, he has the delivery we like, he’s got the makeup, he’s got the size. It’s really hard to poke any holes in this player at all, except for the fact that he’s young, and we really didn’t want to hold that against him.”

There’s that makeup word again.

“It’s one of the most difficult things to evaluate,” Elias said. “But the ingredients that go into that, work ethic, determination, having goals, demonstrating discipline in one’s life, you know, exhibiting a sense of maturity and poise at such a young age, it’s not something you see all the time.”

MLB Network invites top draft prospects to their New Jersey studio, where they can be on-hand for the live draft telecast. Aiken didn’t go for two reasons: he owed it to his teammates to stick around as playoffs unfolded, and he wanted to be with his family.

“We just wanted to keep it close with the family,” Aiken said. “We didn’t really want to do anything too big, we didn’t want to be too flashy. We just wanted to have it close with our family, and also our baseball team was still in playoffs so if we would have won on Tuesday — which it looked like we were going to, but we lost on a walkoff home run, we would have played on Thursday.”

Said Cooper: “All I can tell you is that Houston is (not only) getting the best player in the draft, but they’re getting the best person in the draft.”

Aiken has never been to a game at Minute Maid Park, although he has family in the area and has been to Houston. He’s committed to UCLA, but that shouldn’t matter now.

The first overall pick this year has a signing-bonus value of $7,922,100, but the Astros could redeploy some of that money elsewhere in the draft if Aiken is agree able to a lower bonus. That’s the strategy the Astros took in 2012, signing Correa on the cheap and saving for other early picks.

Luhnow said there was no rush to get a deal done. Draftees have a July 18 deadline to sign a contract.

As Luhnow walked into the Minute Maid press conference following Aiken’s selection Thursday, he received a phone call that was perfectly if not purposely timed.

“Couldn’t be happier to have you,” Luhnow told Aiken. “I remember meeting you in the parking lot of your school. Who knew this would all be happening so quickly? Well, congratulations, you deserved it and we’ll be talking soon I’m sure. Bo (Porter) asked me to find out if you’re available to pitch tomorrow night.”